Hurricane Hunting Drones Probe Storms' Anatomy

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WALLOPS ISLAND, Va. — Off the coast of Bermuda, in the North
Atlantic Ocean, Tropical Storm Gabrielle is churning. More than
700 miles (1,100 kilometers) away, here on a quiet island on the
East Coast of the United States, NASA scientists on Tuesday
(Sept. 10) were preparing to study the storm, using a drone that
can fly above the swirling mass of clouds to examine how they
form and grow.

NASA's Global Hawk airplanes are designed to help researchers
peer inside hurricanes and
tropical storms, enabling them to witness the life cycles of
these extreme weather events. These observations will assist
scientists in developing more accurate models projecting the path
of these storms, and determine whether or not they will gather
strength.

" Forecasting
the tracks of hurricanes has improved over the last several
decades," said Scott Braun, the patriarch and principal
investigator of NASA's Hurricane and Severe Storm Sentinel, or
HS3, mission. "That's because, for the most part, the track is
governed by large-scale winds that steer the storm, and we've
gotten better and better observations over the years, and [we
have] better models for predicting the track. Intensification,
though, is a much more difficult problem." [ In
Photos: NASA's Global Hawk Hurricane Drones ]

This is because a storm's intensity is driven by multiple
factors, ranging from large-scale elements — such as the same
storm-steering winds used to map a hurricane's track — to
smaller-scale and more localized features that occur across only
a few hundred kilometers, such as how individual clouds organize
themselves into bigger cloud systems, Braun explained.

"Small-scale effects are difficult to observe in space and time,"
Braun told LiveScience. "Part of the reason for flying the
aircraft over, or into, these storms is to get more information
about what's happening inside the storms, and how they contribute
to storm formation and intensification."

Eyes in the sky

The
Global Hawk drones are built to fly at altitudes higher than
55,000 feet (16,700 meters), and are capable of performing long
flights that can last up to 30 hours. The bodies and V-shaped
tails of the all-white planes are relatively small, but these
drones boast incredible 116-foot (35-meter) wingspans. Radar and
microwave instruments are housed in the planes' rounded nose and
along their slender bellies.

At NASA's facility here on Wallops Island, the HS3 mission
operates two Global Hawks: one to observe the storm's
environment, and the other to study the structures and processes
within.

The combined altitude and duration of
Global Hawk flights are what make their observations so
valuable to scientists, said Chris Naftel, the soft-spoken but
judicious project manager who oversees the Global Hawk program
from NASA's Dryden Flight Research Center in Edwards, Calif. The
drones also boast impressive range, being able to cover much of
the western Atlantic Ocean and Gulf of Mexico from Wallops
Island. [ Image
Gallery: Hurricane Season 2013 ]

"Our advantage is we can follow a storm for 18 to 20 hours, and
get continuous coverage," Naftel said. "Scientists can also get
all that data in real-time."

On Tuesday morning, Braun and his colleagues planned for a
22-hour Global Hawk mission to study Tropical Storm Gabrielle.

The drone sped down the runway and took off into the pristine
blue sky shortly before 10 a.m. EDT (7 a.m. PDT). But 40 minutes
into the flight, mission operators discovered that one of the
plane's four navigation systems had failed. Despite having three
other functioning systems onboard, the HS3 team decided to
command the Global Hawk to turn around and return to its base in
Virginia.

"The rules for this situation is that we return and land as soon
as possible," Naftel said.

But, since the plane was outfitted to fly a 22-hour mission, it
was still loaded with heavy fuel. To prepare for the early
landing, Global Hawk pilots programmed the drone to fly laps over
the ocean to burn off some of the fuel.

Naftel is unsure what caused the glitch in the navigation system,
but said the unit will be switched out with a spare once the
Global Hawk is on the ground again. Engineers will troubleshoot
the failed system, and the flight over Gabrielle will likely be
rescheduled for later this week.

Watching the Atlantic basin

NASA scientists have been flying Global Hawks over Gabrielle
since before the tropical storm officially formed south of Puerto
Rico a week ago, but the storm quickly petered out, and was
downgraded to a tropical depression a day later. But the
once-disorganized
storm re-formed over the Atlantic Ocean earlier this week,
and battered Bermuda with heavy wind and rain Tuesday night. It
is now churning northward and could impact Nova Scotia and
Newfoundland.

In addition to gleaning information about the tropical storm
itself, the researchers are interested in studying the effect of
an air mass called the Saharan
Air Layer. This hot, dry and dusty air blows over the ocean
from Africa, and may play a role in whether a tropical storm
becomes a hurricane, but the extent of the effect is unknown, and
hotly contested.

"Over the years, there's been arguments to suggest that the
Saharan Air Layer is a positive influence on storm growth,
because it provides a source of energy for the African waves to
become hurricanes," Braun said. "But others have argued that it
can actually be a negative influence on storm growth, by getting
dry air into the storms or suppressing convection overall. So
there's debate in terms of how important it is, one way or the
other, in terms of its impact."

While Global Hawk scientists focus on Gabrielle, the former
Tropical Storm Humberto was upgraded to a hurricane yesterday
morning (Sept. 11). Humberto became the first hurricane of the
2013 season, missing out on the title of latest-forming first
hurricane in the modern record by mere hours.

Global Hawk drones could fly over Humberto, but its location in
the eastern Atlantic Ocean means scientists would only be able to
conduct a 6-hour sortie over the storm, which Braun and his
colleagues determined is too short to be scientifically
worthwhile.

Still, the researchers will be keeping an eye on Humberto's
progress. Sept. 10 was the
climatological "peak" of the hurricane season, which on
average is the date with the most activity in the Atlantic basin,
but this year has seen a somewhat lackluster start.

"An active season was predicted, but 2013 has been a relatively
inactive season so far," Braun said.